Selected components of a prior art magnetic disk drive 10 are illustrated in FIG. 1. A slider 13 containing magnetic transducers (heads) 12 for reading and writing magnetic transitions is urged toward the rotating disk 16 by a suspension (not shown). As the disk rotates an air-bearing develops under the slider and causes it to fly. The slider has an overcoat 15 which provides corrosion protection for the metals in the magnetic transducers 12. The disk 16 typically includes a thin film overcoat 17 and a set of thin films 18 which include one or more ferromagnetic layers in which information is recorded. The average vertical distance between the overcoat over the magnetic read sensor and the disk surface is typically called the element fly-height (FH). Slider clearance is used to mean the amount of fly-height drop allowed before head-disk contact occurs between the lower points of the slider surface and the asperities of the disk. The magnetic spacing between the read and write elements and the disk ferromagnetic material includes two overcoats 15, 17 and the fly-height. A disk drive can contain multiple disks and multiple sliders. The slider 13 contains heater 14 which is used to affect the fly-height of the slider by causing a local thermal expansion of the slider in the area where the read and write heads are located. The thermal expansion has the effect of pushing the transducers closer to the disk and reducing the spacing between the ferromagnetic recording material in the disk and the active components in the slider. A lower slider fly-height and lower magnetic spacing is required for higher areal densities. Fly-heights of less than 7 nm are currently needed. Also the overcoats are made as thin as possible to reduce magnetic spacing. Each slider heater has an adjustable power control element (not shown) in series with it. The thermal expansion induced by a heater can be used in several ways. One use is to compensate during read operations for the similar effect which occurs during a write operation. The electrical current in the write coil causes a thermal protrusion with pushes the write head closer to the media.
Since the dimensions of magnetic sensors are currently on a nanometer scale, the surface topography has become more significant. In one phase of processing the air-bearing surface (ABS) of the slider is typically lapped to a highly smooth surface by mechanical standards, but the resulting surface is nevertheless somewhat irregular on a nanometer scale as is suggested in FIG. 1. In addition to the roughness, the materials in the transducers 12 are typically much softer than the surrounding slider body 19 and tend to be recessed from the general plane of the ABS after slider fabrication. This recession contributes to the spacing between the magnetic sensor in the transducer and the magnetic material in the disk and is, therefore, undesirable. The slider also flies at a slight pitch angle, for example, 100 micro-radians, may have a slight roll, and the ABS may not be perfectly flat so the lowest point on the slider may not be near the transducers.
In US patent application 2003/0174430 by Takahasi, et al., a disk drive with heaters in the slider is described. The heaters include a heating coil and a thermal expansion element. Two heaters are disposed on opposite sides of the transducers (heads). A temperature sensor near the heads is included. The heating coils are electrically connected through the wirings disposed in the arm assembly to a power source and the control unit. Current is supplied from the power source to the coils under control of the control unit. The control unit has a fly-height detection unit, a fly-height control unit, a power supplying control unit, and a converting unit.
US patent application 20040021980 by Albrecht, et al., describes a disk drive with a self-limiting wear contact type air-bearing slider. The magnetic elements of the read/write head extend into and are surrounded by a wearable pad that protrudes beyond the air-bearing surface of the slider. The end of the protruding pad and the ends of the magnetic elements are covered by a corrosion-resistant overcoat that protects the magnetic elements during slider fabrication and disk drive assembly. The overcoated protrusion pad sliders are assembled into the disk drive in a special environment, typically air with humidity controlled below a level above which corrosion of the magnetic elements would occur. The drive is then hermetically sealed. When the slider and disk are first engaged, the disk will be rotated at a reduced RPM (or reduced atmospheric pressure) so that the pad will interfere with the disk surface, which is typically formed of amorphous carbon, and wear down to a selected level. When this level is reached, the wear will be self-limiting and not continue further because of the support provided by the ABS at the reduced disk RPM. When the wear point is reached the overcoat will be completely removed from the pad, thereby exposing the magnetic elements. This initial wear-in process takes place fairly rapidly, typically within about thirty minutes. When the disk is then rotated at full RPM during normal operation of the disk drive there will be a small, well-defined clearance between the magnetic elements and the disk. The result is a head/disk interface which is near contact or zero interference to provide a very small magnetic spacing and which can be reproduced with a wide range of manufacturing tolerances.
US patent application 20040029488 by Gordon Smith describes a method of burnishing a rear pad of a slider within a disk drive. The rear pad is formed of a burnishable material and contains the transducers for reading and writing. The slider is moved in a radial fashion relative to the disk surface in a reciprocal fashion, causing the rear pad to rock. As the rear pad rocks, contact between the rear pad and the disk surface burnishes the rear pad. As a result, a positive camber is imparted in the rear pad relative to the magnetic sensor element. The method can be practiced following initial manufacture of the disk drive, or at various times over the life of the disk drive. In one embodiment, the method includes establishing a radial acceleration of the slider in the first burnishing mode of operation as greater than a radial acceleration of the slider under normal operational conditions of the disk drive. In another embodiment, the disk rotational speed is varied to further enhance burnishing.
In US patent application 20030184916 by Hanchi, et al., the contact interface of the slider is textured to provide a relatively high wear rate to form a self-adjusting fly height interface. Head-disk contact between the textured slider area burnishes the surface of the slider. The burnished portion provides a profile to transition from a contact regime to a fly height regime. Typically, the slider body is formed of an Al2O3—TiC material and the transducer portion includes an Al2O3 (alumina) transducer portion encapsulating the transducer elements. The textured structure is formed on the relative soft Al2O3 portion using interference lithography techniques or laser holography to provide a desired wear rate and a self-adjusting fly height transition.
In US patent application 20020126416 by Gordon Smith a combined magnetic data and burnish head for magnetic recording is described. A burnishing operation is initiated using magnetic force means in the suspension to force the slider below a normal fly-height. The rotational speed of the disk can be substantially less than the rotational speed of the disk during normal read/write operation. In one embodiment, the disk is rotated between about 2500 rpm and about 5000 rpm during the burnishing operation and at about 10,000 rpm during the normal read/write operation. During burnishing operation, the burnishing element physically contacts and removes contaminant particles and/or or other disk surface irregularities.
In the conventional process for fabricating sliders thin film structures for a plurality of heads are fabricated on a wafer. The individual sliders are cut from the wafer and the cut surfaces containing the heads is further processed to become the ABS. The structures on the ABS are critical in determining the flying characteristics of the slider. The range of conditions under which sliders must perform properly include the different surface velocity of the disk at the inner diameter (ID) versus the outer diameter (OD) and the skew introduced by the arcuate path of the actuator which positions the slider over the disk. The ideal features on the ABS are, therefore, not symmetrical. The cut surface of the slider includes a large area of the substrate material which is typically a composite ceramic Al2O3/TiC of an N58 wafer. The features related to the flying characteristic (sometimes called “rails”) are formed by etching the substrate material adjacent to the heads. Two levels of etching are currently used. A dual level etching process is described in US patent application 20030128471 by Bolasna, et al. A dual etch depth slider air bearing surface is described that includes a front pad, a rear pad, and a skewed center rail connecting the front pad to the rear pad. Extending above the rear pad is a V-shaped ABS pad and extending above the front pad are two leading edge ABS pads that are separated by a channel towards the longitudinal center of the slider. The design is said to enable the slider to fly much higher over the landing zone of the disk than at the data zone and provides for a steep take off profile followed by a rapid descend over the data zone.